<?php
namespace lib\wxbiz\aes;
use lib\wxbiz\aes\Pkcs7Encoder;
use lib\wxbiz\aes\ErrorCode;
/**
 * Prpcrypt class
 *
 * 提供接收和推送给公众平台消息的加解密接口.
 */
class Prpcrypt
{

    public $key;

    function __construct($k)
    {
        $this->key = base64_decode($k . "=");
    }

    /**
     * 对明文进行加密
     * 
     * @param string $text
     *            需要加密的明文
     * @return string 加密后的密文
     */
    public function encrypt($text, $corpid)
    {
        try {
            // 获得16位随机字符串，填充到明文之前
            $random = $this->getRandomStr();
            $text = $random . pack("N", strlen($text)) . $text . $corpid;
            // 网络字节序
            $size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
            $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            $iv = substr($this->key, 0, 16);
            // 使用自定义的填充方式对明文进行补位填充
            $pkc_encoder = new Pkcs7Encoder();
            $text = $pkc_encoder->encode($text);
            mcrypt_generic_init($module, $this->key, $iv);
            // 加密
            $encrypted = mcrypt_generic($module, $text);
            mcrypt_generic_deinit($module);
            mcrypt_module_close($module);
            
            // print(base64_encode($encrypted));
            // 使用BASE64对加密后的字符串进行编码
            return array(
                ErrorCode::$OK,
                base64_encode($encrypted)
            );
        } catch (Exception $e) {
            print $e;
            return array(
                ErrorCode::$EncryptAESError,
                null
            );
        }
    }

    /**
     * 对密文进行解密
     * 
     * @param string $encrypted
     *            需要解密的密文
     * @return string 解密得到的明文
     */
    public function decrypt($encrypted, $corpid)
    {
        try {
            // 使用BASE64对需要解密的字符串进行解码
            $ciphertext_dec = base64_decode($encrypted);
            $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            $iv = substr($this->key, 0, 16);
            mcrypt_generic_init($module, $this->key, $iv);
            
            // 解密
            $decrypted = mdecrypt_generic($module, $ciphertext_dec);
            mcrypt_generic_deinit($module);
            mcrypt_module_close($module);
        } catch (Exception $e) {
            return array(
                ErrorCode::$DecryptAESError,
                null
            );
        }
        
        try {
            // 去除补位字符
            $pkc_encoder = new Pkcs7Encoder();
            $result = $pkc_encoder->decode($decrypted);
            // 去除16位随机字符串,网络字节序和AppId
            if (strlen($result) < 16)
                return "";
            $content = substr($result, 16, strlen($result));
            $len_list = unpack("N", substr($content, 0, 4));
            $xml_len = $len_list[1];
            $xml_content = substr($content, 4, $xml_len);
            $from_corpid = substr($content, $xml_len + 4);
        } catch (Exception $e) {
            print $e;
            return array(
                ErrorCode::$IllegalBuffer,
                null
            );
        }
        if ($from_corpid != $corpid)
            return array(
                ErrorCode::$ValidateCorpidError,
                null
            );
        return array(
            0,
            $xml_content
        );
    }

    /**
     * 随机生成16位字符串
     * 
     * @return string 生成的字符串
     */
    function getRandomStr()
    {
        $str = "";
        $str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
        $max = strlen($str_pol) - 1;
        for ($i = 0; $i < 16; $i ++) {
            $str .= $str_pol[mt_rand(0, $max)];
        }
        return $str;
    }
}
